This invention relates generally to radiation detection systems and more particularly to such systems that are arranged for direct viewing and imaging and that incorporate an infrared quantum counter.
Quantum counters or converters that are responsive to infrared radiations have been known in the past, and one such system is disclosed in Bloembergen U.S. Pat. No. 3,070,698. Detecting systems based on such converters commonly include the salt of a selected rare earth element which is arranged to receive incident infrared radiations, the rare earth ion becoming excited from its ground state to a higher energy state in response. This excitation may subsequently decay by radiative or non-radiative energy transitions to a relatively long-lived metastable state. It is also known in the prior art to induce transitions from the metastable state to a still higher energy level by means of an auxiliary source of optical energy commonly referred to as pump radiation. The latter may be either continuously operating or pulsed. Radiative transitions from the higher energy level result in the emission of fluorescent signals at either visible or near-infrared wavelengths.
The described quantum counters have presented the potential for combination with detectors that are sensitive in the near-infrared and visible spectrums with resultant economies in fabrication and heightened sensitivity compared with systems incorporating detectors which are directly responsive to infrared radiation. Despite the apparent advantages, prior art detection systems incorporating infrared quantum counters have not been widely utilized because they have exhibited an undesirably high level of spurious signals or "noise."
Accordingly, an important object of the present invention is to provide a radiation detecting system which incorporates a quantum counter but which nevertheless exhibits high sensitivity and a high signal-to-noise ratio.
A more general object of the invention is to provide a new and improved radiation detecting system.
A more detailed object of the invention is to provide an infrared imaging system having no moving parts.
A further object of the invention is to provide means for temporally discriminating against spurious fluorescence produced within or external to a quantum mechanical substance by pump radiation.
These and other objects and features of the invention will become more apparent from a consideration of the following descriptions.